I thought some of the comments furiously flying about were
a bit uhm.. misleading and in the interest of clarification
and without the permission of Adobe I'd like to quote from the
"PostScript Language Reference Manual"
Second Edition
ISBN 0-201-18127-4
quote
G.2 Document Manager Services
A document manager can provide a wide variety of services. The
types of services are grouped into five management categories:
spool, resource, error, print, and page management. The DSC help
facilitate these services. A document that conforms to this
specification can expect to receive any of these services,
if available; one that does not conform may not receive any service.
..........
G.3 DSC Conformance
The PostScript interpreter does not distinguish between PostScript
language page descriptions that do or do not conform to the DSC.
However the structural information communicated through DSC comments
is of considerable inportance to document managers that operate on
PoscScript page description as data. Because document managers
cannot usually interpret the PostScript language directly, they
must rely on the DSC comments to properly manipulate the document.
It is necessary to distinguish between those documents that conform
to the DSC and those that do not.
G.3.1 Conforming Documents
..........
A conforming document is recognized by the header comment
%!PS-Adobe-3.0
......
G.3.2 Non-Conforming Documents
.........
A non-conforming document is recognized by the %! header comment.
.....
Appendix G.4 Document Structure Rules
G.4.5 Convention Categories
Header Comments
Header comments appear first in a document file, before
any of the executable PostScript language instructions
and before the procedure definitions.
........
All instances of lines beginning with %! after the first
instance are ignore by document managers.
........
endqote
In other words, these "comments" are meant to be machine readeable and
are syntacticaly defined by the language. And though not needed by
the final interpreter, they provide the support needed to the printing
environment.
In the case of a "Document Printing System" for lack of any
other terms, by convention and definition, if the first line of the file
starts with the dreaded "%!", that document is forwarded to the
PostScript interpreter filter, wherever it might be.
Any file coming into that filter has to contain PostScript
commands or else it will generate errors or just be ignored by the
interpreter. And that is whether or not it starts with "%!".
In order to print a PostScript file as actual lines of text then that
file must itsel be converted to PostScript format or else it will
print as originally intended.
Some printers accept both plain text as well as PostScript files and these
systems require that the PostScript documents start with "%!" but again
this is only because the filter selection is being done internally.
As to the reason why that PeeCee File Loader includes a ^D at the
beginning of their PostScript files is due to the fact they have the
unfortunate habit of crashing at unexpected and odd intervals and
the EOF flushes the buffers of the printer's interpreter.
Patrick Arnoux